Struct IbpCrossRowSource 

pub struct IbpCrossRowSource {
    pub r: usize,
    pub d: Array1<f64>,
    pub entries: Vec<(usize, usize, f64)>,
}

Exact cross-row low-rank IBP source (#1038): the per-column rank-one Hessian terms H_(i,k),(j,k) = d_k·z'_ik·z'_jk (for ALL i,j, including the i=j self term) that couple DISTINCT latent rows through a shared atom column k.

Stacking over rows, this is H_full = H₀' + U D Uᵀ, where:

• U is delta_t_len × R with U[g, k] = z'_ik at the global latent index g of row i’s logit slot for atom k (zero elsewhere) — i.e. column k is supported on the atom-k logit slot of every row;
• D = diag(d_k), d_k = w·s'_k (gam_terms::analytic_penalties::IbpHessianDiagThirdChannels::cross_row_d);
• H₀' is the assembled latent block-diagonal H₀ with the per-row self term d_k·z'_ik² REMOVED from each logit-slot diagonal (the assembled H₀ already carries it, so the FULL rank-one outer product U D Uᵀ — which re-adds the i=j diagonal — would double-count without this downdate). The determinant lemma log det(I_R + D UᵀH₀'⁻¹U) is only the exact rank-R correction against this no-self base.

The arrow elimination assumes each row’s H_tt^(i) is independent of every other row, so it structurally cannot hold this coupling block-locally. The factorization owner (solver::arrow_schur) consumes this source to (a) downdate the per-row logit diagonal before factoring, (b) build U/D onto the resulting ArrowFactorCache as a CrossRowWoodbury, and (c) apply the exact Woodbury correction to the value/curvature solve, the evidence log-determinant, and the θ/ρ-adjoint TOGETHER (they all describe the SAME H_full).

Fields

r: usize

Number of atom columns R (the rank of the cross-row update).

d: Array1<f64>

d_k = w·s'_k, the scalar D-coefficient of column k. Length R.

entries: Vec<(usize, usize, f64)>

Per-row column entries (global_t_index, atom_k, z'_ik): each tuple places z'_ik at U[global_t_index, atom_k]. The global_t_index is row_offsets[i] + local_slot for the row’s logit slot of atom k. Only nonzero entries are listed (one per active (row, atom) pair).

Trait Implementations

impl Clone for IbpCrossRowSource

fn clone(&self) -> IbpCrossRowSource

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for IbpCrossRowSource

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for IbpCrossRowSource

fn default() -> IbpCrossRowSource

Returns the “default value” for a type.